Techniques for fabricating large grained single crystal or polycrystalline silicon thin films using sequential lateral solidification are known in the art. For example, in U.S. patent application Ser. No. 09/390,537, the entire disclosure of which is incorporated herein by reference herein and which is assigned to the common assignee of the present application, particularly advantageous apparatus and methods for growing large grained polycrystalline or single crystal silicon structures using energy-controllable laser pulses and small-scale translation of a silicon sample to implement sequential lateral solidification have been disclosed. The sequential lateral solidification techniques and systems described therein provide that low defect density crystalline silicon films can be produced on those substrates that do not permit epitaxial regrowth, upon which high performance microelectronic devices can be fabricated.
While the above-identified patent document discloses a particularly advantageous system for implementing sequential lateral solidification, there have been attempts to modify other systems to implement sequential lateral solidification. One such system is disclosed in U.S. Pat. No. 5,285,236 (“the '236 patent”), the entire disclosure of which is incorporated herein by reference.
Referring to FIG. 1, the '236 patent discloses a 1:1 projection irradiation system. In particular, an illumination system 20 of this projection irradiation system generates a homogenized laser beam which passes through an optical system 22, a mask 14, a projection lens and a reversing unit to be incident on a substrate sample 10. However, in this prior art projection irradiation system, the energy density on the mask 14 must be greater than the energy density on the substrate 10. This is problematical when processes requiring high fluence on the substrate 10 are considered, as the high energy density incident on the mask 14 can cause physical damage to the mask 14. In addition, such high energy laser light can cause damage to the optics of the system. Accordingly, there exists a need for an improved projection irradiation system of the type described in the '236 patent for implementing the sequential lateral solidification process without damaging the mask 14.